I had a look around on Ultimate Retro and there are a bunch of boards with a very similar layout, with as you already found the Biostar the closest match https://www.ultimateretro.net/en/motherboards/9737
As you say, the traces all look to be there, so maybe you can add some real cache. The differences I can see:
RN1,5,6,4 and 7,8,9 are all bigger than need be. Possibly not a problem, except that 1,5,4,6 all block RP19&20.
RP19&20 are fitted on the Biostar boards (and another board that has space on the PCB for them).
R66 should be removed and R65 fitted (looks to be 10k).
JP7,33,9,10 all need to be fitted.
U21,22 need to be fitted (and those two link resistors removed).
Similarish boards with photos, in no particular order:
https://www.ultimateretro.net/en/motherboards/5495
https://www.ultimateretro.net/en/motherboards/640
https://www.ultimateretro.net/en/motherboards/9737
https://www.ultimateretro.net/en/motherboards/10007
https://www.ultimateretro.net/en/motherboards/6825
https://www.ultimateretro.net/en/motherboards/6827
https://www.ultimateretro.net/en/motherboards/4670
Main problem is not knowing what RP19 and 20 should be. I assume they're some sort of bus termination resistor pack. Maybe someone with a similar board could see if they have any markings on the side.
I took snippets of the boards area and aligned them all, so it should be possible to flick between them to see what changes (there are a couple more in the .zip file):
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[edit: just to add, the clock generator UM9515-01 (which I can't find a datasheet for, along with most UMC stuff) looks like it's probably compatible with the MX8315, which there is a datasheet for and it gives a few more possible clock options: https://www.datasheetarchive.com/pdf/download … e=O&term=MX8315 . So the board can (maybe) do 20,25,33,40,50,60,66 and 80MHz.
I did compare a bit more with the Biostar board and it looks like the handful of other changes are mostly to do with changing from using an external RTC to using what I guess is an internal one on one of the UMC chips. For which there are no datasheets]